Continuous low pressure decarboxylation of fatty acids to fuel-range hydrocarbons with in situ hydrogen production

Abstract

Fatty acids are considered as a renewable feedstock for the production of high value products such as fuel-range hydrocarbons. Decarboxylation can produce high quality fuels from fatty acids, although either high pressure or additional hydrogen is required. This study investigated a low pressure (<500psi) continuous decarboxylation process examining oleic acid in a continuous fixed bed reactor using activated carbon, which gave surprisingly high quality fuel-like hydrocarbons with no external hydrogen. The results showed that activated carbon performed as a catalyst for both decarboxylation and in situ hydrogen production. The reaction parameters for maximum degree of decarboxylation (91%) was found to be 400°C, 2h and water-to-oleic acid ratio of 4:1. To determine the degree of decarboxylation and reaction mechanism, the formed liquid products were examined by ATR-FTIR, Raman and GC-FID analysis, respectively. The liquid product was found to consist of mainly saturated hydrocarbons containing heptadecane (89.3% selectivity) as the major compound. The liquid product was found to have a similar density and higher heating value (HHV) to commercial diesel and jet fuel. The mechanism for decarboxylation reaction along with in situ hydrogen formation was proposed in this study.